The ability to organize observed behavior according to its intentional structure is central to understanding, remembering, and learning from other people's actions. This ability requires segmenting ongoing behavior into distinct intentional actions, and recognizing how these actions are organized as necessary steps toward achieving a single goal. For example, actions of peeling, slicing, and putting an apple on a plate serve the larger goal of eating an apple. How does this ability originate and what are the mechanisms behind it? A first series of experiments will explore infants' ability to organize observed behavior according to its intentional structure. Using two different looking-time methodologies, these experiments test whether 12-month-olds, like adults, perceive a set of related actions as a unified whole. A second series of experiments investigates whether low-level physical information assists people in organizing observed behavior. These experiments test whether adults exploit certain physical "cues" to organize unfamiliar behavior, and whether these same physical "cues" assist infants in organizing observed behavior. [unreadable] [unreadable] [unreadable]